1. Field of the Invention
The present invention relates to a solar cell device, particularly relates to a technology for manufacturing a solar cell device having high photovoltaic conversion efficiency at low cost.
2. Description of Prior Art
A solar cell device is expected to replace fossil fuel such as petroleum and coal and to be a new energy source because it can provide clean energy without depletion. In recent year, a solar cell device for generating power for household etc. has been developed and commercialized. A solar cell device, which uses a thin film semiconductor of such as an amorphous semiconductor, is easy to increase its area, and consequently research and development of such a solar cell device have been promoted.
A structure in FIG. 9 is proposed as an example of an element of the thin film solar cell device. In FIG. 9, a substrate 21 having a rough surface for scattering light can be a substrate formed by laminating a metal layer of such as Ag and Al on a flat glass substrate with tin oxide (SnO2), indium tin oxide (ITO), or zinc oxide (ZnO) interposed therebetween, a metal substrate having a rough surface, or a metal substrate coated with a metal layer having a rough surface. A photovoltaic conversion layer 22 composed of a thin semiconductor film containing mainly amorphous silicon, microcrystalline silicon or the like is formed on the substrate 21, and a transparent electrode layer 23 formed of transparent conductive material such as ITO is formed thereon. In this structure of the solar cell device, incident light such as sunlight is incident from a side of the transparent electrode film 23 formed of transparent conductive material such as ITO.
A thin film solar cell device provided with a fine rough surface on a surface of a transparent substrate capable of improving photovoltaic conversion efficiency by the aid of light confinement is also well known.
When transparent conductive material such as SnO2, ITO, and ZnO having a rough shape is used to coat the glass substrate to form the substrate 21, in the solar cell device with thin film, however, cost for forming the rough shape is high, resulting in increase in total cost for the substrate.
When a metal substrate such as stainless steel is used as the substrate 21, difficulty in forming a rough shape on the surface of the metal substrate prevents reduction of cost for the thin film solar cell. In addition, reproducibility of the rough shape is not good.
Furthermore, the substrate 21 of the solar cell device is heavy. When the solar cell device is made larger to generate power, the heavy weight of the solar cell module degrades workability.
It is an objective of the invention to solve the above existing problems and to provide an inexpensive and lightweight solar cell device while obtaining high throughput in forming the rough surface.
A solar cell device according to this invention includes a photovoltaic layer of a thin film semiconductor layer having semiconductor junction in an inside formed on a metal foil formed by electroforming.
The metal foil formed by electroforming has a rough shape of approximately 0.1-10 xcexcm, more preferably 0.1-5 xcexcm, of mean roughness depth (Rz) on a surface of the metal foil.
This invention can provide a solar cell device for power generation capable of reducing cost for manufacture because through put in forming a rough shape, and cost for the rough-shaped metal foil substrate which is electroformed is less as compared with a substrate of a glass coated with the transparent conductive material of such as tin oxide, indium tin oxide, and zinc oxide. Furthermore, the thin film solar cell device using the rough-shaped substrate formed of a metal foil is light-weighted. Therefore, even when the size of the solar cell module increases, the weight is relatively small and workability is good.
A transparent conductive material layer can be interposed between the metal foil and the thin film semiconductor layer.
A conductive material layer and the transparent conductive material layer of high optical reflectivity can be interposed between the metal foil and the thin film semiconductor layer.
A rough shape of approximately 0.02-0.5 xcexcm of mean roughness depth (Rz) can be formed on a surface of the transparent conductive material layer.
The transparent conductive material layer of such as tin oxide, indium tin oxide, and zinc oxide having a fine rough shape can be formed on the metal foil substrate. With this shape of the transparent conductive material layer, incident light such as sunlight can be effectively utilized and efficiency of the solar cell improves.